Conventional imaging apparatuses of this kind have a structure described in JP2001-245186 A, for example. In the structure, a semiconductor imaging device configured of a CCD (Charge Coupled Device) or the like is mounted with a lens on a three-dimensional substrate and converts a focused image formed by the lens into an electric signal so that the image can be output.
The three-dimensional substrate is composed of a base part having a rectangular planar shape and a cylindrical barrel part disposed on an upper portion of the base part, and an opening is formed on a boundary between the base part and the barrel part. The lens is fitted against an inner peripheral surface of the barrel part. With an optical axis of the lens being the center, an optical filter is disposed on an upper side of the opening, and the semiconductor imaging device is disposed on a lower side of the opening.
According to the requirement for a size reduction and a higher performance of portable equipment mounting imaging apparatuses, there has been an increasing demand that the imaging apparatuses themselves be reduced in size and weight. In order to meet this demand, it has been the case that the thickness of each of the above-described components is reduced to the maximum extent, thereby realizing the thickness reduction of imaging apparatuses.
Such a conventional imaging apparatus provides a reduced margin of strength due to the thickness reduction of each constituent component. Because of this, in a heating process for bonding or joining, the flatness of a surface of a three-dimensional substrate on which a semiconductor imaging device is mounted is likely to be deteriorated due to anisotropy in thermal expansion of the substrate and heat distortion caused in the substrate.
Furthermore, semiconductor imaging devices also should be reduced in thickness, and this has been met by so-called back grinding in which a semiconductor wafer is ground from a back surface thereof with, for example, a grinder using a diamond grindstone or the like. Because of this, the mechanical strength of a semiconductor imaging device itself is decreased compared with a conventional case, and the strength of a three-dimensional substrate on which the semiconductor imaging device is mounted also is decreased, so that it is more likely that the semiconductor imaging device and the three-dimensional substrate are warped due to heat and a load applied at the time of mounting.
As described above, thickness reduction leads to an increase in the occurrence of a failure in a process, which causes a cost increase, and requires an inspection process, which increases the number of processes. This has been a hindrance to the thickness reduction of imaging apparatuses. Particularly, with respect to the following problems that are attributable to an entire module being heated/cooled in a bonding or sealing process for fabricating an imaging apparatus, thickness reduction exerts a greater influence on the performance of the imaging apparatus.
That is, when an entire module is heated/cooled, expansion/contraction of air is caused in a cavity enclosed by a semiconductor imaging device and an optical filter that are installed on a three-dimensional substrate. If there is no air circulation from and to the exterior at this time, an internal pressure in the cavity increases and may cause the optical filter to be broken. In order to avoid this, conventionally, an air purging hole is provided so as to communicate with the cavity.
However, with the air purging hole communicating with the cavity, foreign matter may enter the cavity from the exterior via an airflow caused by the expansion/contraction of air. Further, this configuration requires an operation of closing the hole after a bonding or sealing process, and, therefore, foreign matter generated by a material used to dose the hole or foreign matter produced in the closing operation may enter into the inside of the module to cause a flaw in an image.